1. Field of the Invention
The present invention relates to a chip electronic component and a mounting structure therefor, for use with a piezoelectric resonator or a piezoelectric filter and, more particularly, the present invention relates to a chip electronic component and a mounting structure therefor with improved external electrodes provided on the outer surface of an electronic component element.
2. Description of the Related Art
Conventionally, various chip electronic components are used to achieve high-density mounting.
An example of the related art is disclosed in Japanese Unexamined Patent Application Publication No. 3-258107, which discloses a chip electronic component having a pair of external electrodes provided on both ends of a rectangular electronic component element. In this chip electronic component, the external electrodes located at both ends are arranged to be wound on the upper surface, a pair of side surfaces, and the lower surface on the respective ends of the electronic component element, and also to cover both end surfaces thereof. In the same publication, another electronic component is described as including external electrodes that are arranged such that they do not extend to the end surfaces.
Japanese Unexamined Patent Application Publication No. 6-224681 discloses a chip piezoelectric resonant having three external electrodes on the outer surface of a piezoelectric resonant having a rectangular board shape. This chip piezoelectric resonator has a pair of external electrodes provided on both ends of the resonator so as to cover the upper surface, a pair of side surfaces, the lower surface and the end surfaces thereof, and the third external electrode is wound between the pair of external electrodes located on both ends so as to cover the upper surface, a pair of side surfaces and the lower surface thereof. In case where the lower surface is a surface on which the electronic component is mounted, the third external electrode is provided on the upper surface with a recessed portion and a projected portion, each having a width different from that of the remaining portion. The third electrode is arranged to take a capacitance out and so that a desired capacitance may be obtained by adjusting the size of a recessed portion and a projecting portion provided on the upper surface thereof.
When the capacitance is increased, the width of the recessed portion and the projecting portion are increased as well, whereby it is situated closer to the external electrode on the other end. However, the width of the third external electrode on the lower surface (mounting surface) is reduced to prevent short-circuiting.
In addition, disclosed in Japanese Unexamined Patent Application Publication No. 5-83074 is a chip electronic component including a piezoelectric element mounted on a case substrate, and a metallic cap bonded on the case substrate such that it surrounds the piezoelectric element. In the chip electronic component of this type, the case substrate is provided with a through hole electrode, one end of which is electrically connected to the piezoelectric element and the other end of which extends to the lower surface of the case substrate. By arranging the portion of the through hole electrode to extend to the lower surface of the case substrate, the chip electronic component can be mounted on the surface of the printed circuit board. Therefore, it is bonded to the printed circuit board by soldering between the lower surface of the case substrate and the printed circuit board.
When the chip electronic component described in the related art section of Japanese Unexamined Patent Application Publication NO. 3-258107 is mounted on the printed circuit board, the presence of the external electrodes on the side surfaces and the end surfaces of the electronic component element results in formation of a solder fillet thereon. In other words, a solder fillet is formed along the side surfaces and end surfaces of the electronic component element extending in a direction that is perpendicular to the printed circuit board. Therefore, the distances between adjacent chip electronic components cannot be reduced, and thus, high-density mounting is prevented.
Due to formation of the solder fillet, when warpage occurs on the printed circuit board, the chip electronic components are susceptible to a stress caused by the solder fillet. As a result, the bonded portions between the solder fillet and the chip electronic components are susceptible to separation. In addition, the costs of the external electrodes are increased because the external electrodes are arranged to cover the end surfaces in addition to the upper surface, the pair of side surfaces, and the lower surface.
On the other hand, in the chip electronic component disclosed in Japanese Unexamined Patent Application Publication No. 3-258107, the external electrodes do not cover the end surfaces. Therefore, the cost of the external electrodes is reduced in comparison with the chip electronic component disclosed in Japanese Unexamined Patent Application Publication No. 3-258107. However, because the three external electrodes are wound on the upper surface, the pair of side surfaces, and the lower surface of the electronic components, when component is mounted on the printed circuit board, solder tends to deposit along the portion of the external electrode located on the side surface of the electronic component elements and thereby forming solder fillets. Therefore, when warpage of the printed circuit board occurs in the direction of the width of the electronic component element, the chip electronic component is susceptible to an external stress caused by the solder fillets, thereby being susceptible to separation of the bonded portion between solder and the chip electronic components.
High density mounting is possible in the longitudinal direction because solder fillets are not formed on the end surfaces on both longitudinal ends of the electronic component element. However, in the direction of width, formation of solder fillets prevents high-density mounting.
In the chip electronic component disclosed in Japanese Unexamined Patent Application Publication No. 5-83074, the circuit provided in the electronic components is led to the bottom surface of the case substrate via a through hole electrode. Therefore, it is not necessary to provide the external electrode on the side surfaces and the end surfaces of the case. As a result, the mounting density in the direction of both length and width of the electronic component is increased. In addition, since no external electrode exists on the side surfaces and the end surfaces of the case substrate, solder fillets are not formed. Thus, stress caused by warpage of the printed circuit board is reduced in the chip electronic component, thereby increasing stability of the bonded portion.
However, in this type of the chip electronic component, through hole electrodes must be formed on the case substrate, which increases the complexity of the manufacturing process of the case substrate. Further, the mechanical strength of the case substrate decreases due to formation of through hole electrodes.
To overcome the above-described problems, preferred embodiments of the present invention provide a chip electronic component and a mounting structure for the same that is not susceptible to stress caused by warpage of the substrate on which it is mounted, thereby ensuring a reliable electrical connection and a strong mechanical bond, and, further, simplifying the manufacture of the chip electronic component and mounting structure thereof, without requiring complicated manufacturing processes.
A chip electronic component according to a first preferred embodiment of the present invention includes a circuit provided in the electronic component, an electronic component element having a lower surface and a pair of side surfaces, and a plurality of external electrodes arranged to extend over the lower surface and to at least one of the side surfaces of the electronic component element and electrically connected to the circuit therein, wherein each external electrode portion provided on the lower surface of the electric component element is provided with a narrow portion and a wide portion.
In a specific aspect of the chip electronic component according to the first preferred embodiment of the present invention, the relation L1 less than L2 less than L3 is preferably satisfied, where L1 is the width of the external electrode portion located on the side surface of the electric component element, L2 is the width of the narrow portion, and L3 is the width of the wide portion.
The chip electronic component according to a second preferred embodiment of the present invention preferably includes a circuit provided in the electronic component, an electronic component element having a lower surface and a pair of side surfaces, and a plurality of external electrodes arranged to extend over the lower surface and at least one of the side surfaces of the electronic component element and electrically connected to the circuit therein, wherein each external electrode portion on the lower surface of the electronic component element is arranged to have a substantially uniform width from one longitudinal end to the other longitudinal end, and satisfies the relation L1 less than L3, where L3 is the width of the external electrode portion on the lower surface of the electronic component element, and L1 is the width of the external electrode portion provided on the side surface of the electronic component element.
In the first and second preferred embodiments of the present invention, electronic components having various functions can be used, however, in one specific preferred embodiment of the present invention, a piezoelectric resonant component is preferably constructed.
Although the piezoelectric resonant component described above may have various configurations, the component preferably includes a piezoelectric resonant element and a first case substrate provided on at least one surface of the piezoelectric resonant element bonded so as not to interfere with the vibration of the piezoelectric resonant element of the first and second preferred embodiments of the present invention.
According to another preferred embodiment of the invention, the second case substrate is laminated on the upper surface of the piezoelectric resonant element so as not to interfere with the vibration of the piezoelectric resonant element.
According to another preferred of the present invention, the chip electronic component is provided with a cap member mounted on the upper surface of the first case substrate such that it surrounds the piezoelectric resonant element.
The mounting structure of the chip electronic component according to preferred embodiments of the present invention includes a printed circuit board, and a chip electronic component according to preferred embodiments of the present invention mounted on the printed circuit board via a conductive bond, wherein the bonded portion provided by the conductive bond is located inside of the outer periphery of the chip electronic component as seen from the top of the chip electronic component.